https://leetcode.cn/problems/backspace-string-compare/
class Solution {
public:
    bool backspaceCompare(string s, string t) {
        return changeStr(s)==changeStr(t);
    }

    string changeStr(const string& s)
    {
        string ret;
        for(auto& ch:s)
        {
            if(ch!='#')
                ret+=ch;
            else
                if(ret.size())
                    ret.pop_back();
        }
        cout<<ret<<endl;
        return ret;
    }
};